Electron probe analysis employing X-ray spectrography



ELECTRON PROBE ANALYSIS EMPLOYING X-RAY SPECTROGRAPHY Filed oct. 8,19.43

Patented Mar. 25, 1947 ELao'raoN PROBE ANALYSIS EMPLoYiNG X-RAYSPECTROGRAPHY .I ames Hillier, Granbury, N. J assignor` to RadioCorporation of America, a

Ware

corporation of Dela- .appucaaon ottenere, 1943, serial No.5o5,573

7 Claims. (CL 25d-49.5)

This invention relates generally to electron optics and moreparticularly. to X-ray spectrographic means for analyzing materialsirradiated by an electron beam having minute cross-sectional area,

Investigation of the characteristics of various materials by X-rayanalysis is Well known. However', theinstant invention contemplates aunique improvement upon existing methods of X-ray analysis wherein aminute cross-sectional area of the surface of the material underobservation is subjected `to irradiation by an extremely ne beam of highvelocity electrons. The X-rays generated by the impingement otthe highvelocity electrons uponthe minute electron irradiated material surfacearea are A.analyzed by means of any conventional photcgraphicorelectrical X-ray spectrographic apparatus. From the wavelengths ofthepcharacteristic radiation of the material, the` elements thereof maybe determined., hence a point analysis of the specimen is desirab'l`e.

X-ray spectroscopes of the type described in X-rays in Theory andExperiment by Compton and Allison, may be employed to Vanalyze the X-rayradiation derived from the material under observation. The Von Laue typespectrometer, employing a zinc blonde crystal for forming a` diffractionpattern of the X-ray radiationupon a photographic plate, provides asatisfactory permanent record of the X-ray spectrographiccharacteristics of the material. Similarly, the Bragg type spectrometer,also described in 'the reference mentioned heretofore, employs anionizationV chamber for indicating the X-ray refractionTi-rom a zincblende crystal the angular relation of which is adjustable with respectto the axis of the derived X-ray radiation. Various other types of X-rayspectroscopes or X-ray spectrometers may be employed toequal advantage.

The instant invention is related to apnlicants copending U S.application, Ser. No. 505,572, led October 8, .1.943, which describesseveral methods of and means for electron irradiating extremely minuteareas of either electron permeable or electron opaque substances. Thiscopending application describes several methods oi and means for makinga velocity analysis of electrons transmitted by or reiiected from saidelectron irradiated area. The instant invention contemplates means forspectrcanalyzing X-ray radiation de rived from a minute electronirradiated area of substances which may or may not be substantiallyopaque to electrons.

Among the objects of the invention are to provide an improved method ofand means for micro- 2 scopically analyzing materials. `Another objectof .the invention is to provide an improved method of and means formicroscopically analyzingnia-` terals substantially opaqueto`irradiating elec- 5 trons. A further object of the invention is toprovide animproved method of and means for microscopically analyzingmaterials by subjecting minute' areas of' said materials to highvelocity electron irradiation, and spectroanalyzing X-rays generated inthe vicinity of said electronic irradiation. A Further objects oftheinventionjinclude improved means for electron'v irradiating minuteareas of a substance to generate X-rays there.-` from and photographicX-ray spectrographic means for providing al permanentl record of theX-ray spectrographic characteristics of the said material'. Anadditionalobject of the invention is to provide an improved means for electronirradiating a* minute area of a material to generate Xfrays therefromand electrical means for spec,- trcanalyzing said Xf-ray radiation. Theinvention will be further described` by ref-V erence to the accompanyingdrawing of which the single iigure is a schematic, diagram of a typicalembodiment thereof.,

Referring to the drawing, an electron source I, which may comprise, forexample, a thermionic cathode and an apertured anode having high 3electron accelerating potentials therebetween, is focused by aconventional electron lens 2 toform a greatly" reduced image 3 of theelectron source llj `The `image 3 is` further vfocused by means of asecond electron lens 4 to form substantially a point image of theelectron source l at thepoint `5 `o`n` the surfacel of `a` material 6tcV be spectroanalyzed. It should be understood that the rst and secondelectron lenses 2, il, respectively, may be of either the conventionalelectromagnetic or electrostatic types employed in electron microscopesand similar apparatus. The electron lenses may be energized by any meansknown in the art.

The electron irradiation of the point 5 on the surface of the electronopaque material 6 provides X-ray radiation in the vicinity of the point5 due to the energy released by the high velocity electrons comprisingthe electron beam. A portion of this X-ray radiation is intercepted. byan X-ray spectroscope 8 of any known type which will provide the desiredX-ray spectroanalysis.

For the purpose of illustration, the X-ray spectroscope 8 shown in thedrawing, comprises `a pair of lead collimating apertures 9, I0 forselecting an extremely minute X-ray beam for spectroanalysis. Theselected X-ray radiation is applied to a crystal II, which may becomposed,`

for example, of zinc blende. The crystal I I is arranged to be orientedwith respect to the X-ray beam, in order that the X-rays may either betransmitted by the crystal or reflected therefrom.-

The Velocity of lthe X-rays impinging upon the crystals II willdetermine the refraction of the X-rays derived from the crystal. TheX-ray radiation derived from the crystal may be applied to aphotographic plate I2, to obtain a spectroscopic pattern characteristicof the material under observation. When employing a photographic platein an X-ray spectroscope, of the type described, it is customary toorient the crystal so that it transmits the applied X-rays to thephotographic plate.

However, if electrical indication of the X-ray characteristics isdesired, an ionization chamber, not shown in the drawing, is substitutedfor the photographic plate I2. The X-rays are reflected from the crystalII, and the current derived from the ionization chamber is indicated interms of the angular orientation of the crystal with respect to the axisof the applied X-rays.

Thus the invention described comprises a novel method of and means forspectroanalyzing eX- tremely minute surface areas of materials byfocusing a high Velocity electron beam upon a minute area of thematerialsurface, and spectroscopically analyzing X-rays generated bysaid electron bombardment.

I claimV as my invention:

y1. The `method of microscopically analyzing the atomic composition ofamaterial comprising electron irradiating a minute cross-sectional areaof said material,generating X-rays in the vicinity of said area inresponse to said irradiation, and spectroanalyzing said generatedX-rays.

A 2. The method of microscopically analyzing the atomic composition of amaterial comprising generating an electron probe of minutecross-sectional area, electron irradiating said material by saidelectron probe, generating X-rays in the vicinity of said area inrespons to vsaid irradiation, and spectroanalyzing said generatedX-rays.

3. A spectroscope for analyzing the atomic composition of a materialincluding means for supporting said material, means for electronirradiating a predetermined minute cross-sectional surface area of saidmaterial to generate X-rays in the vicinity of said irradiation,-andmeans for spectroanalyzing said generated X-rays.

A4 ing an electron probe of minute cross-sectional area, means forsupporting an object, means for irradiating substantially only a minutesurface area of said object by said electron probe to gene Y ating anelectron probe of minute cross-section- 4. A spectroscope includingmeans for generatal area., means for supporting an object, means forirradiating substantially only a minute surface area of said object bysaid electron probe to generate X-rays in the vicinity of said electronirradiation, and photographic means for spectroanalyzing said generatedX-rays.

6. A spectroscope including means for generating an electron probe ofminute cross-sectional area, means for supporting an object, means forirradiatingsaid object by said electron probe to generate X-rays in theVicinity of said electron irradiation, and photographic means and anX-ray refracting crystal disposed intermediate said object and saidphotographic means for spectroanalyzing said generated X-rays.

7. A spectrometer for analyzing the atomic composition of a materialincluding means for supporting said material, means for electron.irradiating s-ubstantially only a predetermined minute cross-sectionalsurface area of said material to generate X-rays in the vicinity of saidirradiation, and electrical means for spectroanalyzing said generatedX-rays.

. JAMES HILLIER..

REFERENCES CITED The following references are of lrecord in the iile ofthis paten Y UNITED STATES PATENTSV Number Name Date 2,079,900 Cohn May11, 1937 2,131,536 Knoll et al Sept. 27,1938 2,281,325 Ramo Apr. 28,1942 1,971,277 Rupp Aug. 21, 1934 2,341,108 McLachlan Feb. 8, 19442,025,488 Yap Dec. 24, 1935 2,257,774 Von Ardenne Oct. 7, 1941 1,596,305Rentschler Aug. 17, 1926 1,997,356 Bryant Apr. 9,1935 2,197,033 DielsApr. 16,1940 2,274,215 Ruska Feb. 24,1942

FOREIGN PATENTS Number Country Date 86,274 Swiss Aug. 16, 1920

